1. Field of the Invention
The present invention relates to a resistor composition for producing thick film resistors containing (a) a pyrochlore-related oxide of the formula M.sub.x M'.sub.y (Pb,Bi).sub.2-x-y Ru.sub.2 O.sub.7-z, where M=copper and/or silver, M'=calcium, strontium and/or barium, 0.ltoreq.x.ltoreq.0.6, 0.1.ltoreq.y.ltoreq.1.0 and 0.1.ltoreq.z.ltoreq.1.0, and (b) a glass frit.
2. Background Information
German Patent Disclosure DE 39 14 844 A1, (inverntors: Blanke et al., assignee: Heraeus GmbH) U.S. Pat. No. 5,069,824 is a family member of DE 39 14 844 A1; the entire disclosure of U.S. Pat. No. 5,069,824 is incorporated by reference), relates to electrically conductive pyrochlore-related oxides of the general formula M.sub.x M'.sub.y (Pb,Bi).sub.2-x-y Ru.sub.2 O.sub.7-z, where M=copper and/or silver, M'=calcium, strontium and/or barium, 0.ltoreq.x.ltoreq.0.6, 0.1.ltoreq.y.ltoreq.1.0 and 0.1.ltoreq.z.ltoreq.1.0, and to resistor pastes consisting of these oxides, glass frits as dielectric inorganic binders and organic media as liquid vehicles. Thick film resistors which are produced from the resistor pastes of DE 39 14 944 by printing on, for example, aluminum oxide substrates and firing, are distinguished by low HTCR, CTCR and .DELTA. TCR values (HTCR=hot temperature coefficient of resistance, CTCR=cold temperature coefficient of resistance, .DELTA. TCR=HTCR-CTCR). However, it has been shown that these values are subject to comparatively large fluctuations and are particularly affected by the firing temperature.
Resistor pastes for thick film resistors are proposed in EP Patent Disclosure EP 0 013 977 B1 (inventor: Hoffman et al., assignee: DuPont) (EP 0 013 977 E1 is a family member of U.S. Pat. No. 4,302,362, the entire disclosure of U.S. Pat. No. 4,302,362 is incorporated y reference herein) which, in addition to an organic vehicle, essentially consist of 20 to 75 parts by weight of a pyrochlore compound of the general formula (M.sub.x Bi.sub.2-x)(M'.sub.y M".sub.2-y)O.sub.7-z, where M=yttrium, thallium, indium, cadmium, lead, copper, rare earth metals, M'=platinum, titanium, chromium, rhodium, antimony, M"=ruthenium and/or iridium, x=0-2, y=0-0.5 and z=0-1, of 12-75 parts by weight of a glass binder and 2-30 parts by weight of a temperature-resistant finely divided filler. The filler has a thermal expansion coefficient of 40-60.times.10.sup.-7 /.degree.C., a particle size of 0.1 to 3 micrometers and is preferably composed of zircon or mullite. The resistor pastes are printed on dielectric substrates and are fired at 850.degree. C. (peak temperature) in air. As a result of the addition of the filler, the thick film resistors obtained in this manner show improved stability, i.e., in contrast to the resistance drift observed elsewhere, the resistance values remain relatively constant following mechanical stresses, such as occur, for example, during trimming of the resistor by means of a laser beam as a result of the sudden change in temperature. Resistor trimming is defined as the exact setting of the resistance value following firing by abrading resistor material until the desired resistance value has been obtained ("Elektronik-Lexikon", edited by Ernst Baier, 2nd. ed., 688, Stuttgart, Franck'sche Verlagshandlung, 1982).